Summary To investigate cellular processes or model diseases within particular tissues, it is often necessary to manipulate gene expression at the level of single cells or cell clusters. One of the most successful methods for directing gene expression in specific cells is the GAL4?UAS system, where any genetic sequence of interest can be transcribed under the control of UAS regulatory sequences. Transcription from UAS is activated by the binding of GAL4, which can be expressed in a huge variety of patterns by placing its transcription under the control of different gene enhancers. The GAL4?UAS system has been improved to give greater specificity by expressing the GAL4 DNA-binding and activation domains under the control of separate enhancers, causing UAS transcription to occur only in cells where both domains are expressed. This intersectional strategy has been used extensively to identify neuronal circuits in the brain and to manipulate their activities. It has not, however, been used to nearly the same extent in other tissues?particularly in tissues that show high cell turnover. To extend the utility of this ?split-GAL4? system to a self-renewing tissue and to improve Drosophila as a model organism for studying cellular aspects of human epithelial diseases, scientists at the Bloomington Drosophila Stock Center will characterize the expression of split-GAL4 driver transgenes in the intestine. To cut through the complexity of driver expression patterns, they will use the advantages of the split-GAL4 system to restrict UAS expression to individual primary cell types (stem cells and the cell types arising from them) using cell type-specific reference drivers and then document the cell type-specific expression of other drivers in each specialized intestinal region. This innovative approach will simplify driver characterization and introduce efficiencies into the documentation process. Reference drivers specific to each primary cell type will be developed and used to demonstrate that driver expression patterns can be deconstructed by cell type and region as expected (Aim 1). To gain experience using this approach and extend the value of an established resource, the expression patterns of a subset of split-GAL4 drivers from a large collection recently acquired for public distribution will be characterized and used to assemble a set of drivers for directing gene expression in functional intestinal units defined by cell type and region (Aim 2). This stock kit will spur research interest in the intestine by simplifying the design of experiments by individual researchers. Furthermore, the utility of the split- GAL4 system will be extended to the study of dietary, microbial and environmental factors relevant to health and disease by screening for drivers induced specifically by starvation or the ingestion of a pathogen, new microbiome member or harmful chemical (Aim 3). As a resource-development project, this work will generate tools useful to biomedical investigators using Drosophila to investigate fundamental biological processes and model human diseases at the level of single cells. It will benefit the Bloomington Drosophila Stock Center by enhancing its capabilities in developing new research resources.